I looked at the description, but it appears as if it will use only Google. Could I make it use Scroogle or Wikipedia?One way is to use AcidSearch. Once installed, you can set up a number of search engines for easy access via the Preference menu (accessible when you click on the upside down triangle on the Search Window). There, you can make any search engine the default one.
I just tried that one. It has a fixed list of search engines, and I could not see any way to add to that by point and click. I do not know enough about whatever syntax the list has in it to add any more to the package manually.You can change that in the safari.plist file. Easy to do with one of the GUI apps that can adjust various parameters in the Safari settings. Here's one - Safari Enhancer
I still do not understand how to add more search engines than are already in there. The "Import" is looking for plists which I do not have. How am I supposed to add any? I want to add Scroogle and Wikipedia. I see no way to do that.
also - look under the 'Using Advanced features' for the 'importing and exporting channels'Click the "New Channel" button to create a new channel. AcidSearch attempts to automatically create the channel based on the current web page. Double-click on the channel's name in the list to rename it, and press return to save your changes.